IMPAIRMENT OF INTRACORTICAL GABAERGIC INHIBITION IN A RAT MODEL OF ABSENCE EPILEPSY

The WAG/Rij rat strain is characterized in its EEG by the manifestatio n of spike-wave discharges which resemble in their spontaneous appeara nce and pharmacological sensitivity the absence epilepsy observed in h umans. In order to test the hypothesis whether cellular intrinsic memb rane and/or synaptic network properties in the neocortex are modified in this form of epilepsy, we analyzed with extra- and intracellular re cording techniques the functional status of neocortical slices obtaine d from adult epileptic WAG/Rij rats and compared them with the data ac quired from non-epileptic control Wistar rats. Intrinsic membrane prop erties, like resting membrane potential, neuronal input resistance and basic cellular firing characteristics, did not differ between these t wo strains. However, the analysis of extra- and intracellularly record ed synaptic responses revealed an intracortical hyperexcitability whic h was accompanied by a significant reduction in the efficiency of GABA ergic inhibition. Our data indicate that the imbalance between intraco rtical excitatory and inhibitory mechanisms may at least contribute to the expression and augmentation of spike-wave discharges in epileptic WAG/Rij rats.